# What is the largest apparent size a moon of a habitable planet can have? [duplicate]

Inspired by this question: How large can an apparent size of a moon be?

I am looking for a moon that is:

1. a terrestrial moon with properties vaguely similar to Luna (not a binary planet, but it can be a minor moon as long as it’s spherical enough)
2. Host planet is not tidally-locked to the moon
3. The moon does not cause tides or tidal heating so significant as to make the host planet uninhabitable
4. The moon is not beyond the Roche limit (otherwise the moon would break apart)
5. Could possibly form naturally (even if rare/unlikely).

Feel free to change the orbit distance and size of the moon as needed as long as it fulfils the above requirements and maximises the apparent size of the moon to observers on the planet. The planet’s parameters can be changed as well as long as it can have an atmosphere, liquid water on the surface and could host life (similar to Earth).

I am looking for a set-up vaguely similar to Earth and Luna but with the moon appearing more than 0.5 degrees of the sky.

• They can be changed as well as long as the host planet is habitable (oceans, atmosphere, could host life) Commented Dec 14, 2023 at 0:13
• @sphennings no, because the parameters in the top answers are all binary setups (tidally-locked, similar mass objects). What I am looking for is more akin to Earth-Luna but with the moon appearing much larger in the sky (more than 0.5 degrees of the sky). Commented Dec 14, 2023 at 0:42
• Given that the distinction between binary planets and a planet with a moon is an arbitrary one, you will need to define that distinction for yourself. Given that the equations don't care about whether something is a moon or a planet, you should be able to apply them to your scenario as well. Commented Dec 14, 2023 at 0:45
• Since tidal locking depends on all sorts of things that may or may not apply in your situation, the linked question should be taken to be the answer unless details are added to this question that rule out that question and its answer. Commented Dec 14, 2023 at 0:48
• @MontyWild I am looking for the planet to not be tidally-locked to the moon and for the moon to not cause catastrophic tidal forces. Anything else is fair game. I’ve edited my question to hopefully give a better idea of what I’m asking. Commented Dec 14, 2023 at 0:51